It's all rom sounds. Apart from FX and aftertouch and sustain, there's not much you can do on a G 800, but you can use an expression pedal, like a roland EV-5.
Also very handy for the organ presets.
Fred
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Keyboards/Sound Units: Kurzweil 2600S, Roland VR-760, Acces Virus C, Roland G-800, Akai AX60, Minimoog, Machine Drum, Roland R8-M, mediastation x-76